This invention relates generally to Gatling machine guns and, more specifically, to the class of such guns known as 7.62 miniguns and improvements therein that serve to significantly improve their operational reliability.
The 7.62 minigun is a six-barreled, electric-driven machine gun originally designed and built by General Electric Company in the mid 1960""s for the U.S. military. This gun has been in use since its inception by both the U.S. and foreign military forces, as well. Compared to other small caliber machine guns, the 7.62 minigun is complicated and, under operational conditions, often unreliable.
The 7.62 minigun fires a conventional 7.62 NATO cartridge that includes a bullet, a cylindrical cartridge case, a primer, and powder. The bullet is seated in the open end of the cartridge case; the primer is seated in the center of the base of the cartridge opposite the bullet; and the powder is located inside the cartridge case between the bullet and the primer. The cartridge is fired conventionally by first detonating the primer, which ignites the powder and, in turn, causes pressure within the cartridge case to increase to the point that the bullet is forced out of the cartridge case and down the barrel of the gun.
Cartridges are handled within the gun by six bolt assemblies, one for each of the six barrels. Each of the six bolt assemblies is aligned with a respective one of the six barrels. The six bolt assemblies are attached to and surround a main rotary body known as the rotor. The rotor is the core axis of the gun. The six barrels are connected to the forward portion of the rotor and are arranged for rotation as a cluster about a common axis, coincident with that of the rotor.
The bolt assembly is a mechanism that inserts a loaded cartridge into the barrel chamber and removes the empty cartridge after firing The bolt assembly is generally cylindrical in shape and includes a bolt head, a bolt body, and a spring-loaded firing pin as major components. The bolt head serves to retain the cartridge, while the bolt body houses the firing pin, which extends from the bolt body through the bolt head to provide a common longitudinal axis for both. A single off-center male helical cam extends from the bolt head rearward toward the bolt body, along and around the longitudinal axis of the bolt assembly. The male helical cam terminates in a corresponding groove termed a female helical cam. The male helical cam, in combination with the female helical cam, constitute a helical cam system. During operation of the gun, the bolt head and the bolt body are compressed together along the central axis created by the firing pin. During this process, the firing pin spring is compressed. As the bolt head and bolt body are compressed, the helical cam system forces the bolt head to rotate. At a predetermined point of rotation, a latching mechanism releases the spring-loaded firing pin, allowing it to strike the primer.
It is not uncommon for the male helical cam to break during use, causing the gun to severely jam. As a result of the use of only one helical cam system that is not aligned with the longitudinal forces of the cylindrical bolt assembly, the male helical cam is subjected to excessive asymmetric loads which, over time, cause it to fail. Another disadvantageous byproduct of the asymmetric loads resulting from the use of a single helical cam system is the tendency toward longitudinal centerline misalignment of the bolt head and the bolt body, which causes the firing pin to strike the primer of the cartridge off center. This periodically results in late detonation or complete failure of detonation of loaded cartridges. Failure of detonation results in live ammunition being discarded and causes the gun to run rough. The likely result of late detonation is severe jamming of the gun.
It would therefore be advantageous to provide a machine gun in which malfunctions due to component breakage are reduced by reducing the asymmetric forces acting on the male helical cam. It would also be advantageous to provide such a gun in which the firing pin strikes the center of the cartridge primer with higher accuracy and consistency than in previous designs, to thereby prevent late detonation or total failure of detonation at all of the cartridge.
These and other advantages are provided in accordance with the illustrated embodiment of the present invention by incorporating a second male helical cam to the bolt head, opposite the existing male helical cam. Correspondingly, a second female helical cam is positioned in the bolt body, opposite the existing female helical cam, for receiving the second male helical cam. The combination of the second male and female helical cams forms a second helical cam system. In addition to the second helical cam system, a bearing pads are added to the bottom of the bolt head to support the bolt head, under certain circumstances, in the chamber area of the forward portion of the rotor. More specifically, the bearing pads provide a positive means for ensuring proper alignment of the bolt head to the bolt body, in turn ensuring proper alignment of the firing pin with the center of the primer. Under normal circumstances, the combination of the two helical cam systems will provide the desired alignment of the firing pin and primer. However, in the case of excessive wear of the bolt assembly, for example, the bearing pads will come in contact with and be supported by the chamber area of the rotor to ensure that the centerline of the bolt head will remain within an acceptable range.